Results obtained through a series of competitive displacement experiments verified CD44/α1(IV)1263–1277PA liposome recognition [23, 62]. More specifically, α1(IV)1263–1277PA liposomal rhodamine delivery correlated with cellular CD44 content and was inhibited in a dose-dependent fashion by exogenous α1(IV)1263–1277PA [23]. Fluorescence microscopy revealed localization of α1(IV)1263–1277PA liposomes to CD44-positive cells [62]. In the present study, we further modified DSPG/DSPC liposomes with the addition of PEG. Such modifications have previously

been shown to increase liposome circulation times in vivo [53, 76–82]. We used 5mol % of PEG-2000 Inhibitors,research,lifescience,medical in our liposomes (Table 1), the same amount of PEG used in the clinically approved drug Doxil (DOX encapsulated PEG-stabilized liposomes) [83]. The size of the PEG chain chosen took into account the size of the PEG used in Doxil (PEG-2000) [83], as well as the impact PEGs of various sizes could have on our system specifically. Previous studies suggested that increased circulation Inhibitors,research,lifescience,medical times

can be achieved with increasing PEG chain lengths up to PEG-5000 [77, 84, 85]. However, we chose not to utilize PEG larger than 2000Da for three reasons. First, it has Inhibitors,research,lifescience,medical been shown that rigid liposomes composed of DSPC (as is the case here) exhibit a drop off in circulation times when PEG greater than 2000Da is incorporated due to chain entanglement and lipid phase separation resulting in increased opsonization [85–88]. Second, previous work using membranes containing a mixture of the α1(IV)1263–1277PA and PEGs of various sizes resulted in binding of M14#5 human melanoma cells when Inhibitors,research,lifescience,medical PEG-120,

PEG-750, or PEG-2000 were used, but not with PEG-5000 [89]. Neutron reflectivity data revealed head group lengths of 8.8, 9.0, and 16.8nm for α1(IV)1263–1277PA, DSPE-PEG-2000, and DSPE-PEG-5000, respectively [89]. The lack of binding Inhibitors,research,lifescience,medical observed with PEG-5000 was thus attributed to the complete masking of the α1(IV)1263–1277PA by the PEG, thereby minimizing ligand accessibility. Third, the presence or absence of 5% PEG-2000 in α1(IV)1263–1277PA/DMPC (1:19) liposomes had little effect many on the delivery of Texas Red to CD44-positive fibroblasts [62]. In the present study, cells were directly exposed to each liposomal system and free DOX and incubated at 37°C. In this environment, free DOX can be taken up by cells more rapidly than liposome encapsulated DOX. However, free DOX was not as efficacious as CD44 targeted liposome encapsulated DOX towards M14#5 melanoma cells (Figure 5). Thus, the targeting strategy promoted more efficient DOX delivery in vitro. Further supporting this conclusion was the observed correlation between the cytotoxic effect of DOX-loaded targeted liposomes and CD44/CSPG content for M14#5 and BJ cell lines. Eliaz and Szoka Jr. developed CD44-targeted liposomes using HA GSK1349572 nmr fragments (see Section 1) [20].